would this be a decent 5.1 system

I know everything should be good but i'm not sure about the surround speakers (i'm trying to cut a little bit of cost). Do you think them will do the trick?

Receiver

Onkyo 606

Fronts
Polk Audio RTi8

Center
Polk Audio CSi3

Sub
Polk AudioPSW10

Rears
Polk Audio RM6751